Vitamin
Vitamin K
Also known as: K1, Phylloquinone, Phytonadione, Vitamin K
A fat-soluble vitamin essential for blood clotting, bone metabolism, and cardiovascular health. Phytonadione (K1) is the plant-derived form found in leafy greens and the primary supplemental form.
Last reviewed June 2026 · Evidence graded from peer-reviewed research, not editorial opinion. Educational only — not medical advice.
Every Vitamin K product we have scored
| # | Product | Score | Per serving |
|---|---|---|---|
| 1 | Thorne Vitamin D + K2 Liquid | 96 A | $0.06 |
| 2 | Thorne Vitamin K | 93 A | $0.52 |
| 3 | Pure Encapsulations Calcium K/D | 92 A | $0.53 |
| 4 | NOW Foods Mega D-3 & MK-7 | 91 A | $0.28 |
| 5 | Codeage A D K Vitamins | 90 A | $0.25 |
| 6 | Nutricost Vitamin K2 + Vitamin D3 | 90 A | $0.12 |
| 7 | Swanson Real Food Vitamin K2 - Maximum Strength | 90 A | $1.27 |
| 8 | Sports Research D3 + K2, Plant-Based | 89 A | $0.37 |
| 9 | Thorne Advanced Nutrients | 88 A | $2.40 |
| 10 | Thorne Basic Nutrients 2/Day | 88 A | $0.60 |
| 11 | Thorne Basic Prenatal | 88 A | $1.23 |
| 12 | Life Extension Vitamins D and K with Sea-Iodine | 87 A | $0.30 |
Scored on dose accuracy, form, label transparency and third-party testing. Per-serving cost is list price divided by servings per container. No brand pays to be listed or ranked.
Common questions
How much Vitamin K should I take?
The typical range is 90-120 mcg daily (RDA). Usually adequate from diet
When should I take Vitamin K?
With fat. Yes.
Which form of Vitamin K is best?
Tablet — Standard form. Other forms in the catalog: Phytonadione (K1), Menaquinone (K2), Phylloquinone.
Is Vitamin K safe?
Commonly reported: Very safe. Serious warnings: CRITICAL: Reverses warfarin anticoagulant effect, Warfarin users must consult physician before use, Keep vitamin K intake consistent if on blood thinners. Safe
Which Vitamin K supplement scores highest?
Thorne Vitamin D + K2 Liquid, at 96/100. Scored on dose accuracy, form, label transparency and third-party testing — no brand pays to be listed or ranked.
Daily target & upper limit
120 mcg / dayVitamin K has an established daily reference intake. See best forms, label synonyms, upper-limit warnings, and top-scoring supplements:
Vitamin K dosage reference →Primary uses
- Blood clotting
- Coagulation support
- Blood clotting support
- Bone health and mineralization
- Cardiovascular health
- Protein carboxylation
How it works
- Essential cofactor for clotting factors II, VII, IX, X
- Rapidly cleared from circulation
- Converts to MK-4 in some tissues
Dosage
- Typical range
- 90-120 mcg daily (RDA)
- Timing
- With fat
- With food
- Yes
- Duration
- Usually adequate from diet
- Special populations
- Those on warfarin need consistent intake
Forms
- Tablet
- Phytonadione (K1)· 70/100
- Menaquinone (K2)· 70/100
- Phylloquinone· 70/100
Safety
Common side effects
- Very safe
Contraindications
- Warfarin users (without physician guidance)
- Other vitamin K antagonist anticoagulants
Products containing Vitamin K
Top-scoring supplements in our catalog that list Vitamin K on the label. Each product is graded on Formulate's ingredient-level rubric — dose accuracy, form, transparency, and third-party testing.
Known interactions
Evidence notes
Essential for coagulation
Grade A: Multiple well-designed human trials support the main claims.
Cited research for Vitamin K
Clinical studies referenced across Formulate guides that mention vitamin k. Each links to the full study page with PubMed source + the guides that cite it.
- Violi et al. (2016)Medicine (Baltimore)
Interaction Between Dietary Vitamin K Intake and Anticoagulation by Vitamin K Antagonists: Is It Really True? A Systematic Review
- Yamey et al. (2007)BMJ
Effect of fixed-dose vitamin K supplementation on INR stability in warfarin patients
- Couris et al. (2006)Int J Vitam Nutr Res
Dietary vitamin K variability affects International Normalized Ratio (INR) coagulation indices
Related in Vitamin
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Medical disclaimer. This page is educational and does not replace advice from a qualified healthcare provider. Individual needs and risks vary — consult a professional before starting, stopping, or combining supplements, especially if you are pregnant or nursing, taking medication, or managing a health condition.